Servo-valve



June 17, 1958 s, HOLMES 2,839,079

SERVO-VALVE Filed May 25, 1955 STANLEY b. HOLMES %%4n AL 72. 1/ r :22/795,

United States Patent 6 SERVO-VALVE 7 Stanley H. Holmes, Chicago, 11].

Application May 25, 1955, Serial No. 510,969

Claims. (Cl. 137-622) The present invention relates to a servo valve anda hydraulic control system, and more particularly relates to a valvemechanism and hydraulic control system for controlling bidirectionalfluid actuation of any mechanism to be so actuated.

While it will be understood, of course, that embodiments of the presentinvention are devices and systems of general utility, the servo valveand hydraulic system described in detail hereinbelow embodying theprinciples of this invention are described with reference to theirutilization in a control system for operating such a mechanism as alathe with a tracer or stylus following a template whereby the lathe isoperated to cut in accordance with the contour and configuration of theedge of the template. This illustration and exemplification of anembodiment of present invention has been taken here since it is anexample of installation wherein the present invention may enjoyparticular utility.

Thus, it is an important object and feature of the present invention toprovide a new and improved hydraulic system to control bidirectionalhydraulic actuation. In the illustrated and described embodiment of thisinvention the hydraulic system is effective to control bidirectionalactuation of a piston and cylinder assembly controlling movement of atool block on a lathe.

Another object of the present invention is to provide a new and improvedhydraulic system for controlling hydraulic actuation-and to effectivelyfollow a template.

Another object of the present invention is to provide a new and improvedhydraulic system with a servo valve including means therein to actuatefluid by-pass valves.

Still another object of the present invention is to provide a new andimproved servo valve for an hydraulic system, this valve being operableto control fluid flow through a plurality of outlets in the valve andfrom an inlet into the valve.

Still another object of the present invention is to provide a new andimproved servo valve mechanism with a cylinder having regions ofdiffering internal diameters, alternate regions having the same diameterand adjacent regions having different diameters, and a pistonconfigurated to conform to the regions of a cylinder and means tocontrol resilient reciprocation of the piston whereby fluid flow throughports in the cylinder is controlled.

7 Still another object of the present inventionis to provide. a new andimproved servo valve mechanism with apertured housing segments havingvaried apertures therein, alternate apertures being substantiallyidentical and adjacent apertures being different, and a plurality ofpiston segments assembled together with the piston segments beingdimensioned to correspond to the apertures in the housing segments,means resiliently mounting the piston for axial movement within thecylinder, means to adjust the resilient bias against the piston in onedirection, and means to control axial displacement in the piston wherebyfluid flow through ports in the cylinder is controlled.

Still another object of the present invention is to pro- 2,839,079Patented June 17, 1958 ice vide a new and improved device of the classdescribed with anew and improved actuator operable to actuate themechanism by either longitudinal forces applied thereto or transverseforces applied thereto.

Still another object of the present invention is to provide a new andimproved servo valve of the class described with an actuating platepivotally coupled to the piston in the valve, pivotally coupled to anactuator and pivotally coupled to by-pass control means such as a micrcswitch of the like.

Still another object of the present invention is to provide a new andimproved actuator mechanism for a servo valve of the class described.

Still other objects, features and advantages of the present inventionwill become readily apparent from the following detailed description ofthe present invention and an embodiment thereof, from the claims, andfrom the accompanying drawings in which each and every detail shown isfully and completely disclosed of this part of the specification, inwhich like reference numerals refer to like parts, and in which:

Figure 1 is a more or less diagrammatic plan View of the lathe having atool block actuator and hydraulic control system therefor embodying theprinciples of the present invention:

Figure 2 is an end View of a servo valve for the control system andembodying the principles of this invention; and

Figure 3 is a sectional view of the servo valve of Figure 2 viewed astaken substantially along the line HIlIl of Figure 2.

As shown in the drawings:

There is illustrated in Figure 1 more or less diagrammatically, afragmental portion of a lathe bed 10 carrying a live center mechanism 11and a dead center mechanism 12 between which there is disposed a toolblock 13 operable to traverse the work piece 14 held between a livecenter po nt 15 and a dead center point 16. The tool block carries acutting tool 17 whereby the work piece 14 may be lathe cut to a desiredcontour as the tool block 13 traverses the work piece by riding on thebed 10. In addition, the tool block 13 is movable transversely of thelathe bed 19 whereby contoured configurations may be cut into the workpiece 14.

For transverse movement of the tool block 13 with respect to the bed 10,the tool block base 18 which carries the tool block 13 and rides on thelathe bed 10 is equipped with a double acting piston and cylinderassembly 19 having a piston 26 reciprocably disposed in a cylinder 21and connected to a piston rod 22 which is in turn connected to the toolblock 13 whereby bidirectional operation of the piston and cylinderassembly is transmitted to the tool block 13. The piston and cylinderassembly 19 is connected from its opposite ends through fluid feed tubes23 and 24 to a servo valve mechanism 25 which is provided with a feedtube 26 leading to fluid pump connected to an appropriate reservoir, thevalve 25 also being provided with reservoir return tubes 27 and 2,8.

In operation, the valve 25 is equipped with a template follower stylus29 which follows a template 30 to actuate the valve and thereby controlthe flow of fluid from the inlet tube 26 to the actuating piston andcylinder assembly 19 through the tubes 23 and 24 and to control returnto the reservoir through the tubes 27 and 28. Thus, when the valve ismoved by the movement of the stylus as the same rides on the contourededge of the templates, it supplies fluid to the cap end of the cylinder21 through the feed tube 24, from the pump supply inlet to the tube 26,the tube 23 from the rod end of the cylinder will accommodate returnfluid flow and the valve 25 will permit the return fluid flow to passfrom the tube 23 to the tube 27 to return to the reservoir. When thevalve 25 is actuated in an opposite direction fluid will be suppliedfrom the tube 26 through the tube 23 to'the rod end of the cylinder andthe fluid in the cap end' of the cylinder will return through tube 24and the valve 25 to the reservoir return tube 28.

From the foregoing described operating characteristics of the hydraulicsystem and the servo valve 25, it will be readily understood that thevalve is so operable to control fluid flow to the double acting pistonand cylinder assembly 19 that the tool 17 will describe a path identicalto that-of a contoured edge on the template 30 where by the work piece14 will be cut in accordance with that contour. Should the contour be sosharply configurated that the ordinary operation of the valve 25 mayseem insuflicient to properly actuate double acting piston and cylinderassembly 19, the valve mechanism is provided with an electricallyactuable controlling mechanism whereby'by-pass valves 31 and 32'will beactuated selectively to open the hydraulic feed line 26 directly to thefeed tubes 23 and 24 respectively depending upon the direction ofactuation.

The valve mechanism is a smoothly acting valve V which is operative tometer the volume of oil flowing therethrough and is eifective uponactuation of the stylus to permit full flow in one direction and controlvelocity in the other as well as being effective tocontrol fluid flowpressure. Additionally, the valve mechanism is adjustable for properbalancing thereof whereby the valve operation is extremely smooth.

At the. other end of the housing 35, an actuator mechanism 33 is carriedon an actuator mounting bracket 39 which is securedto the housing 33 byscrews 4% or the like threadably engaging the side Walls of the housing33 The actuator end of the housing 33 is structurally open to receive a,plurality of housing or cylinder segments or disks, successivelyidentified at 41, 42, 43, 44, 45, 46 and 47, which are disposedsuccessively in interfacial engagement with each other and held againsta shoulder 48 within the housing 33 by a clamping ring 49 threadablyengaging the interior of the side walls of the housing 33 at theactuator end thereof. The said disks 41-47 are axially apertured as at41' through 47' and the clampingring 49 is provided with an axialaperture 49. While the dimensions of the apertures 41,

' 47 and 49 in the disks 41 and 47 and the ring 49 are not critical, itis'important that the apertures 42, 44 and 46 in the disks or segments42, 44 and 46 be substantially identically dimensioned and configurated,and that the apertures 43' and 45 in the disks 43 and 45 also besubstantially identically dimensioned and configurated but that theselatter two apertures be larger than the apertures in the rings 42, 44and 46. Thus by this construction, alternate rings have substantiallyidentical, apertures while adjacent rings have difiering apertures andthe intermediate apertures be larger than the central and extremityapertures.

Thi dimensioning, relation and assembly of the segments or disks isimportant for proper operation of the valve mechanism and a propercooperation of the cylinder portion of the valve with the piston portionthereof described immcdiately herein below.

Between end pairs of segments, that is, between the segments 41 and 42and between the'segments 46' and 47, there is clamped a pair ofresilient thin end sealing diaphragms 50 and 51 respectively which sealin the disks 42, 43, 44, 45 and 46, and which resiliently axially carrya piston rod 52 having'an enlargedactuator end 53 abutted 'againsttheouter axial interface of the diasufficiently large diameter to permitabutment thereof by an adjusting spring 6t}. The disks 55 through. 59,however, are critically dimensioned corresponding to the apertures 42'through 46' in the rings 42 through 46 respectively with the pistondisks or segments 55, 57 and 59 which are the central and extremitysegments having identical outside diameters smaller than the insidediameters of the disks 42, 44 and 46 and having axial di mensionswhichare substantially identical to eachjo'therbut greater than the axialdimensions of the disks 42 through 46, which latter disks havesubstantially identical dimensions to each other. The disks 56 and 58,

however, have identical outside diameters substantially 1 larger thanthe outside diameters of the disks 55,57 and 59 but substantiallysmaller than the inside diameters of the disks 43 and 45 and have axialdimensions which are substantially smaller than the axial dimensions ofthe disks 55, 57 and 59 while being dimensioned identia cally with eachother.,. The arrangement of the disks55 through 59 is thus such thatalternate disks are substantially dimensioned whileadjacent disks aredifierently dimensioned and the spacing of thedisks 56 and 58 is suchthat while they are in interfacial engagement with the disks 55, 57 and59, they arealso identically spaced between the radial faces of thedisks 42 and 44, and the disks-44 and 46 respectively. Thatis, the disks56 and 58 are so spaced that the spacing between the, disks 42 and 56 isidentical to the spacing between the disks 44 and 58; and the spacingbetween the disks 56 and 44 is identical to the spacing between thedisks 53 and 46. With this arrangement of the disk segments, any axialdisplacement of the piston assembly will result in identical variationsin'the spacings of the'housing disks and piston disks and, at all times,the spacing at one end of each of the piston disks will be identical andspacing of the other side of the piston disks to the housing disks Thisoperational characteristic of the will be identical. piston disks andcylinder disks permits a proper control of fluid flow within the valvebetween the diaphragms 50 and 51. That is, this characteristic ofactuated operation of the piston assembly permits proper fluid flowcontrol through the ports 27, 23, 26, 24' and 28' which correspond inplacement to the fluid tubes 23 and 24 leading to the double actingpiston cylinder assembly in Figure l, the fluid flow tubes 27 and 28leading to thereservoir, and the fluid tube 26 leading to the valve'mechanism from a fluid supply pump, respectively. These ports extendaxially through the housing 33 and are placed a to meet with annularouter peripheral grooves 42a, 43a,

44a, 45a, and 46a in the outer peripheries of thedisks 42 through 46respectively. Radial apertures 27a,.23a, 26a, 24a and 28a are providedin the disks of 42' through 46 to thereby properly communicate thehousin'gports' 27', 23., 26', 24' and 28' respectively with theapertures and space within the cylinder assembly.

By this arrangement of the ports, the cylinder as-, sembly, and thepiston assembly, movement or axial dis placement of the piston assemblyto the left as viewedv in Figure 3 will act to close rod end ports 23'from the reservoir port 27' and .open the port 23 to the fluid;

supply port 26', while at thesame timelacting to close the cap end port24' from the fluid supply port 26'. and

open the cap end port 24' to the reservoir port 28 by closing the spacebetween the disks 42 and S6'and the space between the disks 44 and 58and at the same time opening the space between disks 56 and 44 andopening the space between the disks 58 and 46. Reverse actuation of thepiston 52 will have a reverse efiect whereby fluid will be supplied fromthe port 26' to the port 24' and the port 23' will be exposed to thereservoir port 27'.

To so actuate the piston, the actuator end of the piston rod is providedwith a pivot head pivotally connecting the same to an actuator plate 61carrying a ball pivot socket member 62 and also pivotally engaging thestrongly resiliently outwardly urged control button 63 of a micro-switchor the like 64 adjustably positionable by an adjusting screw or the like65 mounted on the actuator bracket 39. Here it should be noted that themicroswitch 64 and/or similar mechanisms may be provided herein tooperate the over travel solenoids and bypass valves 31 and 32 and thatwhen it is desired to eliminate the micro-switches and the by-passvalves, an over travel spring may be substituted for the micro switchbetween the actuator plate 61 and the adjusting screw 65. Normally, theresilient bias at the point of engagement of the switch button 63 withthe actuator plate 61 is greater than any axial bias on the pistonassembly provided by the resilient diaphragms 50 and 51 and theadjusting spring 60 so that any actuating force on the actuator plate 61applied through the ball pivot socket 62 efiects axial movement of thepiston assembly for valve actuation. It is only when the limit ofmovement of the piston assembly to the left is reached that furtherforce on the actuating plate ball pivot socket 62 to the left will causeoperation of the micro switch 64 or an over travel spring substitutedtherefor, or a limit or movement of the lower end of the plate 61 isreached the movement of the piston to the right will operate the microswitch.

The stylus and actuator structure is such that a ball 66 is held betweenthe ball pivot socket 62 on the actuator plate 61 and a ball pivotsocket 67 on an inner end of a stylus carrier 68 having a tracer ordirectional stylus 69 secured in the outer end'thereof by set screw orthe like 70. The stylus carrier 68 is resiliently mounted in a stylusbushing 71 by a spring 72 seated against a retainer ring 73 in thestylus bushing and urging the stylus carrier into intershoulderengagement, as at 74, with the stylus bushing 71. The stylus bushing 71is in turn mounted in a ball bearing bushing 75 for substantiallyfrictionless operation and reciprocation therein, the ball bearingbushing being mounted on the actuator bracket 39. The stylus bushing isalso urged resiliently against the ball 66 to retain the same betweenthe ball pivot pockets by a small spring 76 on the inner side of theactuatingbracket 39.

With this structure, any axial inward force on the stylus 69 will betransferred to the ball 66, to the actuated plate 61 and then to thevalve piston assembly, and if the force is of sufiicient strength thenit will also be transferred to the micro-switch 64 or an over travelspring substituted therefor. If the stylus 69 is freed of engagementthen resilient force acting on the piston assembly from the adjustingspring 60 will move the stylus to the right through the force actingthrough the actuator plate 61 and the ball 66, and if travel is carriedbeyond the limit of right hand axial movement of the piston 52, then themicro-switch 64, which may be a switch of the double throw type, isactuated oppositely.

This mechanism is also sensitive to radial force applied on the stylus69 since that will cause relative pivotal movement of the stylus carrierabout the shoulder engagement thereof with the stylus bushing at such apoint as 74 whereby there will be a result of movement in the actuatingplate 61 and thereby in the piston assembly for the valve.

From the foregoing it will be readily deduced that fine adjustment ofthe valve mechanism is important to smooth operation thereof and forthat purpose, the adjustor or adjusting mechanism 35 is so coupled tothe piston assembly as to provide for very fine adjustment of theresilient force applied on the piston through spring 60 and thereby veryfine adjustment of the piston assembly with respect to the cylinderassembly. In this embodiment of the invention the adjusting mechanism 35includes a difierentially threaded internally and externally threadedadjusting screw 77 having its external threads 78 threadably engaging athreaded aperture 79 in the end wall 34 of the housing 33. The outer endof a central aperture 80 in a screw 77 is enlarged to freely receive aninner screw 81 which threadably engages inner threads 32 on the innerend of the screw 77. Further inwardly on the end of the screw 77, thescrew 81 has a flanged spring backing member 83 fixed thereon for axialmovement therewith, the spring backing member 83 operating to confinethe spring 60 of the adjusting mechanism between the end piston disk 54and the spring backing member 83 itself. By difierentially threading thescrew 77 so that, for example, the external threads 78 are about 30threads per inch and the internal threads at 82 are about 32 threads perinch, one revolution or complete turn of the screw 77 by operation ofthe knurled knob 38 thereon at the outer end thereof will result in anaxial movement of the inner screw 81 of about (0.002 inch), the innerscrew 81 being fixed against rotational movement by a hexagonal pin 89fixed therein as at 9% and fixed against rotation while being permittedto move axially by being received in an appropriately configuratedhexagonal aperture 91 in the end of the adjusting support bracket 36.Since the screw 81 has an axial movement which is only the differencebetween the fitting on the two screws, any rough adjustment effected byoperation of the knurled knob 88 will result in a fine axial movement ofthe inner screw 81.

On its innermost end, the screw 81 carries a stopblock 160 which isfixed thereon for axial movement therewith by any such means as beingslidably engaged on the screw. This stop block is fitted for axialmovement within a piston stop 101 which takes the form of a flangedsleeve secured to the end of the piston rod 52 immediately adjacent tothe adjusting mechanism or forming a part of the piston disk 54. Theexposed end 102 of the flanged sleeve and piston stop 101 is radiallyinwardly flanged as shown at 163 whereby it cooperates with the stopblock in the manner immediately hereinafter described.

in operation of the hydraulic system such as is illustrated in Figure 1it is highly desirable to meter a fiuid flow through the servo valve 25when the stylus 29 is moving in a direction to seat the contoured edgeof the template 39. Also, it is highly desirable to limit movement ofthe piston rod 52 in the aforesaid direction to thereby eliminate anypossible fluttering of the valve spool or piston when the stylus engagesthe template. To this end, the stop block 100 and flanged portion 103cooperates to limit'movement of the valve spool or piston to such aposition that when the valve spool or piston is moved to its maximumlimit in a right hand direction as viewed in Figure 3, the piston disks56 and 58 will be held out of engagement with the immediately adjacentfaces of the housing or cylinder disk segment 44 and 46. The adjustingmechanism provides for such a controlled position stop of the piston orvalve spool and permits fine adjustment of the stop since fineadjustment of the axial position of the screw 81 will finally adjust theaxial position of the stop block and thereby finally adjust the positionat which the flanged sleeve or piston stop 101 will engage the stopblock 100 and thereby finally adjust the limit of right hand movement ofthe piston or valve spool 52 as viewed in Figure 3.

From the foregoing it will be readily observed that numerous variationsand modifications may be effective without departing from the truespirit and scope of the novel concepts and principles of this invention.I, there-.

, 7 f fore, intend to cover all such modifications and variations asfollows within the true spirit and scope of the novel conce tsand rinciles of this invention.

I claim as my invention:

1; In a hydraulic system to control bidirectional actuation, a servovalve comprising a plurality of housing segment plates havingrespectively difierent size apertures therein and secured'together withthe apertures coaxially arranged, the apertures in alternate segmentplates being of the same dimensions, a piston resiliently mounted forresilient axially reciprocable movement in the apertures in said segmentplates, said piston being comprised of segments, of different dimensionscorresponding to the apertures in said segment plates and beingalternately of the same dimensions, resilient diaphragms sealing theends of the secured together segmentplates and sealingly and resilientlysupporting said piston, an actuatingplate having pivotal engagement withsaid piston, radial ports leading from certain of said segment pla.es,means to'control displacement of the piston to control fluid flowbetween said ports within the valve by controlling pivotal displacementof the actuating plate, and yieldable overtravel means forming areaction mem-' her for said actuating plate.

2. In an hydraulic actuator control valve, a hollow cylinder havingregions of diifering inside diameters, and fluid ports therein,alternate regions being of substantially the same diameter, a pistonreciprocally disposed in said cylinder, said piston having regions ofdifiering outside diameters corresponding to the regions of thecylinder,

means sealing said piston and said cylinder and resiliently mountingsaid piston coaxially within said cylinder for resilient axialdisplacement, a resilient biasing spring seated against one end of thepiston, differential screw means mounted on the cylinder and abuttingsaid spring and:carrying stop means to finely adjust metering of themovement of the piston, actuating means coupled to the piston to controlaxial displacementof the piston and thereby control fluid flow throughthe ports, and overtravel means forming a reaction member for saidactuating means and yielding upon overtravel of said piston.

33; In an' hydraulic actuator control valve, a hollow cylinder havingregions of differing inside diameters, and fiuid ports therein,alternate regions being of substantially the same diameter, a pistonreciprocably disposed in said cylinder, said piston having regions ofdiffering outside diameters corresponding'to the regions ofthe'cylinder, means seming said piston and said cylinder and resilientlymounting said piston coaxially within said cylinder for resilient axialdisplacement, a pivotal actuating plate coupled to the piston,displacementisensing means coupled to the actuating plate to displacethe'piston upon displacement of the displacement sensing means tocontrol fluid flow through the valve, and overtravel meansforming afulcrum for said actuating plate and yielding-upon overtravel of saidpiston effected by displacement thereof" by said displacement sensingmeans.

4.- In an hydraulic actuator controlwalve ja; hollow cylinder havingregions of differing inside diameters, and j nected to-the actuatingplate to displace said piston, said last mentioned means including adisplacement sensingmember, means biasing said member towards saidactuating plate, ayieldable fulcrum forsaidactuating platecompensatingtor overtravel of said displacement sensing means and'pivotmeans coupling the same to said-actuating platewhereby displacement ofthe sensingmeans operates to displace the piston and thereby controlfluidflow through thevalve. I 9 v 5. In ahydraulic systemto control-bidirectional actuation, a servovalve comprising abousing having aplurality of abutting housing segment plates'withinsaid housing inengagement withi'thewall thereof and having respectively different sizeaxially extending apertures therein andsecured together with theapertures coaxially arranged, the apertures in alternate segment platesbeing 7 of the same dimensions, apiston resiliently mounted for axialreciprocable movement along theapertures in saidhousing segment plates,saidpiston being comprised of segments of difierent dimensionscorresponding; to the apertures in said housing segment plates and beingalternately of the samedimensions, radial ports in said segment plates,radial ports in said housing. in alignment with the ports -in saidsegment plates,1actuating means for said piston controlling displacementthereof and thereby controlling fluid flow within the valve between saidports, and over travel means engaging said actuating means and yieldingupon over travel of said piston and forming a reaction member for saidactuating-means.

References Cited in the 'fileof'this patent UNITED STATES PATENTS 71,575,771 2,075,600 Baker Mar. 30, 1937 2,563,423 Samothrakis -u Aug. 7,1951 r 2,620,823 Adams Dec; 9,1952 2,624,585 Churchill -n Jan. 6, 19532,658,523 Johnson Nov.- 10, 1953 I r 2,696,196 Adams Dec. 7, 19542,699,756 Miller June 18, 1955- FOREIGN PATENTS 586,501 Great Britain1947 King -n; Mar. 9,1926

